Atsushi Sugihashi

Laser welding of metal honeycomb panel with multiple reflecting effects of high power laser beams

We have developed a new method of laser welding to produce honeycomb structures consisting of flat and corrugated metal sheets as shown in Fig.1. The experiments have been conducted using pulsed mode Nd-YAG lasers and CO2 lasers. Specimens are stainless steel sheets, high-alloy corrosion resistant steel sheets or the like, whose thicknesses are from about 50μ m to 1mm. In this method, a laser beam of low energy density, with high reflectance from steel surfaces, is irradiated into the wedge shape space which is formed from both the flat and corrugated metal sheets, and is automatically focused at the top of the wedge shape space by means of multiple reflection effects. Most of the energy of the laser beam can be converted to heat and used to weld the opposed walls of the wedge shape. This laser welding method increases the welding efficiency and improves the quality of the weld joints of the honeycomb panels which could be used for aircraft, super express trains and for the exhaust systems of the internal combustion engines of automobiles.Usually honeycomb panels are produced by brazing or electro-resistance spot welding. However, those processes are complicated and expensive, and the productivity is very low. Using the multiply reflected laser beam welding method, it is possible to realize an effective manufacturing process for these all-welded high performance metal honeycomb panels.We have developed a new method of laser welding to produce honeycomb structures consisting of flat and corrugated metal sheets as shown in Fig.1. The experiments have been conducted using pulsed mode Nd-YAG lasers and CO2 lasers. Specimens are stainless steel sheets, high-alloy corrosion resistant steel sheets or the like, whose thicknesses are from about 50μ m to 1mm. In this method, a laser beam of low energy density, with high reflectance from steel surfaces, is irradiated into the wedge shape space which is formed from both the flat and corrugated metal sheets, and is automatically focused at the top of the wedge shape space by means of multiple reflection effects. Most of the energy of the laser beam can be converted to heat and used to weld the opposed walls of the wedge shape. This laser welding method increases the welding efficiency and improves the quality of the weld joints of the honeycomb panels which could be used for aircraft, super express trains and for the exhaust systems of the internal...

Mechanism of anisotropic stress generation in laser peening process

The purpose of this work is to investigate mechanism of anisotropic residual stress generation in laser peening. Residual stress induced by multiple pulse irradiation is simulated using stress distribution of single pulse. Contribution of each irradiation spot to the stress field is assumed to be additive, and the Mises yield condition is considered as constraint for the field addition process. The result explains well the anisotropic stress generation. The model can be applied to optimize the residual stress field.The purpose of this work is to investigate mechanism of anisotropic residual stress generation in laser peening. Residual stress induced by multiple pulse irradiation is simulated using stress distribution of single pulse. Contribution of each irradiation spot to the stress field is assumed to be additive, and the Mises yield condition is considered as constraint for the field addition process. The result explains well the anisotropic stress generation. The model can be applied to optimize the residual stress field.

Study of metal drilling characteristics with Q-switched CO2 laser

In spite of recent rapid progress of high power solid state laser, CO2 laser systems are still useful for metal drilling with hole diameter of about 100 µm and depth of several tens of µm, because it requires large pulse energy of about 100 mJ with high beam quality. Mechanically Q-switched CO2 laser systems are favorable for such application with high repetition rate (>10 kHz) [1,2] and have the advantage of cost performance.In spite of recent rapid progress of high power solid state laser, CO2 laser systems are still useful for metal drilling with hole diameter of about 100 µm and depth of several tens of µm, because it requires large pulse energy of about 100 mJ with high beam quality. Mechanically Q-switched CO2 laser systems are favorable for such application with high repetition rate (>10 kHz) [1,2] and have the advantage of cost performance.